Solid-phase synthesis of 2,6,8-trisubstituted purines

2,6,8-Trisubstituted purines were synthesized from 2,6-dichloropurine bound to polystyrene-based Rink resin at the N(9) position. Selective successive displacements of the chlorine atoms in the 2- and 6-positions followed. Bromination of C(8) and Stille coupling concluded the synthesis.